TABLE 1

ED₅₀ values (mean ± 1 S.E.M.) for morphine alone and after MCAM in a warm water tail-withdrawal procedure measuring the latency to remove tails from water maintained at 50°C

Dose ratios (95% confidence intervals) are ED₅₀ values for morphine after MCAM divided by ED₅₀ values for morphine before MCAM.

Dosing Condition	ED₅₀	Dose Ratio
	mg/kg
Morphine alone	7.52 ± 0.80
Morphine after 1 mg/kg MCAM
1 day	17.14 ± 2.20	2.38 (1.65, 3.08)^{^a}
5 days	7.95 ± 0.53	1.14 (0.85, 1.41)
Morphine alone	7.52 ± 0.80
Morphine after 3.2 mg/kg MCAM
1 day	68.61 ± 8.95	10.21 (5.77, 14.29)^{^a}
5 days	29.27 ± 0.55	4.47 (2.90, 5.79)^{^a}
9 days	27.38 ± 1.58	4.15 (2.67, 5.39)^{^a}
13 days	17.38 ± 2.73	2.66 (1.28, 3.85)^{^a}
17 days	8.80 ± 0.14	1.33 (0.90, 1.69)
Morphine alone	7.30 ± 0.56
Morphine after 10 mg/kg MCAM
1 day	187.68 ± 7.56	26.76 (21.44, 31.81)^{^a}
5 days	61.68 ± 6.01	8.97 (6.01, 11.65)^{^a}
9 days	41.75 ± 3.90	6.11 (3.94, 8.10)^{^a}
13 days	91.67 ± 10.56	12.65 (9.54, 15.59)^{^a}
17 days	98.95 ± 2.71	14.13 (11.36, 16.78)^{^a}
21 days	100.23 ± 3.90	14.23 (11.60, 16.77)^{^a}
29 days	64.75 ± 8.59	9.29 (5.71, 12.39)^{^a}
37 days	55.06 ± 9.72	7.58 (4.63, 10.15)^{^a}
45 days	35.40 ± 3.06	4.95 (4.05, 5.81)^{^a}
53 days	29.77 ± 0.59	4.25 (3.44, 5.02)^{^a}
69 days	25.73 ± 3.20	3.83 (2.02, 5.53)^{^a}

↵^a Potency of morphine was significantly changed as evidenced by 95% confidence intervals of the potency ratios that did not include 1.